The Iberian Ribbed Newt or Spanish Ribbed Newt (Pleurodeles waltl) is a newt endemic to the Iberian Peninsula and Morocco. It is known for its sharp ribs which can puncture through its sides, and as such is also called the Sharp-ribbed Newt.

In the wild it grows up to 30 cm, but usually only to a 20 cm in captivity. It has a long tail which is about half its body length.

The Iberian Ribbed Newt has tubercles running down each side. Through these, its sharp ribs can puncture. The ribs acts as a defense mechanism, causing little harm to the newt. Ejection of the ribs rarely occurs in captive animals.

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Sex determination

Sex determination is regulated by sex chromosomes, but can be overridden by temperature. Females have both sex chromosomes (Z and W), while males have two copies of the Z chromosome (ZZ). However, when ZW larvae are reared at 32 °C (90 °F) during a particular stages of development (stage 42 to stage 54), they differentiate into functional neomales.

Hormones play an important role during the sex determination process, and the newts can be manipulated to change sex by adding hormones or hormone-inhibitors to the water they are reared in.

Aromatase, an estrogen-synthesizing enzyme which acts as a steroid hormone, plays a key role in sex determination in many non-mammalian vertebrates including the Iberian Ribbed Newt. [2] It is found in higher levels in the gonad–mesonephros complexes in ZW larvae than in their ZZ counterparts, although not in heat-treated ZW larvae. The increase occurs near the final stages of which their sex can be determined by temperature (stage 52).

Conservation

The IUCN listed the Iberian Ribbed Newt as Near Threatened in its 2006 Red List. It received this listing because its wild populations appear to be in significant decline due to widespread habitat loss and the effects of invasive species, thus making the species close to qualifying for Vulnerable. Previously, in 2004, the species had been listed as Least Concern, the lowest ranking. This species is generally threatened through loss of aquatic habitats through drainage, agrochemical pollution, the impacts of livestock (in North African dayas), eutrophication, domestic and industrial contamination, and infrastructure development. It has largely disappeared from coastal areas in Iberia and Morocco close to concentrations of tourism and highly populated areas (such as Madrid). Introduced fish and crayfish (Procambarus clarki) are known to prey on the eggs and larvae of this species, and are implicated in its decline. Mortality on roads has been reported to be a serious threat to some populations.

Space experiments

Pleurodeles waltl has been studied in space on at least six missions. The first Iberian Ribbed Newts in space may have been in 1985 on board Bion 7[3]. The ten newts shared their journey with two Rhesus Macaques and ten rats, in an otherwise crewless Soviet Cosmos satellite. In 1992, Bion 10[4][5] also carried the newts on board, as did Bion 11[6] in 1996.

P. waltl research was continued later in 1996 by French-led experiments on the Mir space station (Mir Cassiopée expedition [10]), with follow-up studies in 1998 (Mir Pégase expedition) and 1999 (Mir Perseus expedition). Foton-M2[7] also carried the Iberian Ribbed Newt in 2005.

The newts were chosen because they are a good model organism for the study of microgravity[8]. They are a good model organism because of the female's ability to retain live sperm in her cloaca for up to 5 months, allowing her to be inseminated on Earth, and later (in space) have fertilisation induced through hormonal stimulation. Another advantage to this species is that development is slow, so all the key stages of ontogenesis can be observed: from the oocyte to swimming tailbud embryos or larvae.

Studies looked at the newts' ability to regenerate (which was faster in space overall, and up to two times in early stages[9]), as well as the stages of development and reproduction in space[10].

On the ground, studies of hypergravity (up to 3g) on P. waltl fertilisation have also been conducted[11], as well as on the fertility of the space-born newts once they arrived back on Earth[12] (they were fertile, and without problems).

Other amphibian species to travel in space include the newt species Lissotriton vulgaris and Cynops pyrrhogaster, and frog species: African clawed frog, Japanese tree frog, and several frogs in the Rana genus: Rana pipiens, Rana calestiana and Rana temporaria.